1. Field of the Invention
This invention pertains generally to a method for aggregating a plurality of links to simulate a unitary connection among one or more nodes in a fibre channel system. This invention is particularly, but not exclusively, useful for providing in-order delivery of data frames across the plurality of links without requiring reinitialization of the fabric in a fibre channel system due to variations in link characteristics.
2. Relevant Background
The information explosion of recent decades has, in part, driven requirements for enhanced computer performance that has increased significantly, if not exponentially. Consequently, demand for high-performance communications for server-to-storage and server-to-server networking has increased. Performance improvements in hardware entities, including storage, processors, and workstations, along with the move to distributed architectures such as client/server, have increased the demand for data-intensive and high-speed networking applications. The interconnections between and among these systems, and their input/output devices, require enhanced levels of performance in reliability, speed, and distance. Simultaneously, demands for more robust, highly available, disaster-tolerant computing resources, with ever-increasing speed and memory capabilities, continue unabated.
To satisfy such demands, the computer industry has worked to overcome performance problems often attributable to conventional I/O (“input/output”) device subsystems. Mainframes, supercomputers, mass storage systems, workstations and very high resolution display subsystems frequently are connected to facilitate file and print sharing. Because of the demand for increased speed across such systems, networks and channels conventionally used for connections introduce communication clogging, aptly called “bottlenecks,” especially if data is in large file format typical of graphically based applications.
Efforts to satisfy enhanced performance demands have been, in part, directed to providing storage interconnect solutions that address performance and reliability requirements of modern storage systems. At least three technologies are directed to solving those problems, SCSI (“Small Computer Systems Interface”); SSA (“Serial Storage Architecture”), a technology advanced primarily by IBM; and Fibre Channel (“F/C”), a high performance interconnect technology.
Two prevalent types of data communication connections exist between processors, and between a processor and peripherals. A “channel” provides direct or switched point-to-point connection communicating devices. The primary task of the channels is to transport data at the highest possible data rate, with the least amount of delay. Channels typically perform simple error correction in hardware. A “network”, by contrast, is an aggregation of distributed nodes. A “node” as used in this document is either an individual computer or another machine in a network (workstations, mass storage units, etc.) with a protocol that supports interaction among the nodes. Typically, each node is capable of recognizing error conditions on the network, and provides the error management required to recover from error conditions. Protocols, of course, are analogous to various languages and dialects used in human speech; to the extent that a node can “understand” which protocol is used, all nodes in a system can “speak the same language.” Fibre Channel systems typically are routed using a protocol known as the FCP Protocol, which like protocols in general, includes a data transmission convention encompassing timing, control, formatting, and data representation.
SCSI is an “intelligent” and parallel I/O bus on which various peripheral devices and controllers can exchange information. Although designed approximately 15 years ago, SCSI remains in use. The first SCSI standard, now known as SCSI-1, was adopted in 1986 and originally designed to accommodate up to eight devices at speeds of 5 MB/sec. SCSI standards and technology have been refined and extended frequently, providing ever faster data transfer rates up to 40 MB/sec. SCSI performance has doubled approximately every five years since the original standard was released; and the number of devices permitted on a single bus, for example, has been increased to 16. In addition, backward compatibility has been enhanced, enabling newer devices to coexist on a bus with older devices. Significant problems associated with SCSI remain, however, including, for example, limitations caused by bus speed, bus length, reliability, cost, and device count. In connection with bus length, originally limited to six meters, newer standards requiring even faster transfer rates and higher device populations now place more stringent limitations on bus length that are only partially cured by expensive differential cabling or extenders.
Accordingly, industry designers now seek to solve limitations inherent in SCSI by employing serial device interfaces. Featuring data transfer rates as high as 200 MB/sec, serial interfaces use point-to-point interconnections rather than busses. Serial designs also decrease cable complexity, simplify electrical requirements, and increase reliability. Two solutions have been considered, Serial Storage Architecture (“SSA”) and what has become known as Fibre Channel technology, including the Fibre Channel Arbitrated Loop (“FC-AL”).
Serial Storage Architecture is a high-speed serial interface designed to connect data storage devices, subsystems, servers and workstations. SSA was developed and is promoted as an industry standard by IBM; formal standardization processes began in 1992. Currently, SSA is undergoing approval processes as an ANSI standard. Although the basic transfer rate through an SSA port is only 20 MB/sec, SSA is dual ported and full-duplex, resulting in a maximum aggregate transfer speed of up to 80 MB/sec. SSA connections are carried over thin, shielded, four-wire (two differential pairs) cables, which are less expensive and more flexible than the typical 50- and 68-conductor SCSI cables. Currently, IBM is the only major disk drive manufacturer shipping SSA drives; there has been little industry-wide support for SSA. That is not true of Fibre Channel, which has achieved wide industry support.
Fibre Channel is an industry-standard, high-speed serial data transfer interface used to connect systems and storage in point-to-point or switched topologies. FC-AL technology, developed with storage connectivity in mind, is a recent enhancement that also supports copper media and loops containing up to 126 devices, or nodes. Briefly, fibre channel is a switched protocol that allows concurrent communication among workstations, super computers and various peripherals. The total network bandwidth provided by fibre channel may be on the order of a terabit per second. Fibre channel is capable of transmitting frames along links (also, “lines” or “lanes”) at rates exceeding 1 gigabit per second in at least two directions simultaneously. F/C technology also is able to transport commands and data according to existing protocols such a Internet protocol (“IP”), high performance parallel interface (“HIPPI”), intelligent peripheral interface (“IPI”), and, as indicated using SCSI, over and across both optical fiber and copper cable. Fibre Channel may be considered a channel-network hybrid. A Fibre Channel system contains sufficient network features to provide connectivity, distance and protocol multiplexing, and enough channel features to retain simplicity, repeatable performance and reliable delivery. Fibre channel allows for an active, intelligent interconnection scheme, known as a “fabric,” as well as fibre channel switches to connect nodes.
The F/C fabric includes a plurality of fabric-ports (F_ports) that provide for interconnection and frame transfer between plurality of node-ports (N_ports) attached to associated devices that may include workstations, super computers and/or peripherals. A fabric has the capability of routing frames based on information contained within the frames. The N_port transmits and receives data to and from the fabric. Transmission is isolated from the control protocol so that different topologies (e.g., point-to-point links, rings, multidrop buses, and crosspoint switches) can be implemented. Fibre Channel, a highly reliable, gigabit interconnect technology allows concurrent communications among workstations, mainframes, servers, data storage systems, and other peripherals. F/C technology not only provides interconnect systems for multiple topologies that can scale to a total system bandwidth on the order of a terabit per second, but also can deliver a high level of reliability and throughput. Switches, hubs, storage systems, storage devices, and adapters designed for the F/C environment are available now.
Following a lengthy review of existing equipment and standards, the Fibre Channel standards group realized that it would be useful for channels and networks to share the same fiber. (The terms “fiber” or “fibre” are used synonymously, and include both optical and copper cables.) A Fibre Channel protocol was developed and adopted, and continues to be developed, as the American National Standard for Information Systems (“ANSI”). See Fibre Channel Physical and Signaling Interface, Revision 4.2, American National Standard for Information Systems (ANSI) (1993) for a detailed discussion of the fibre channel standards, which is incorporated by reference into this document.
Current standards for F/C support bandwidth of 133 Mb/sec, 266 Mb/sec, 532 Mb/sec, 1.0625 Gb/sec, and 2 Gb/sec (proposed) at distances of up to ten kilometers. Fibre Channel's current maximum data rate at 1.0625 Gb/sec is 100 MB/sec (200 MB/sec full-duplex) after accounting for overhead. In addition to strong channel characteristics, Fibre Channel provides powerful networking capabilities, allowing switches and hubs to interconnect systems and storage into tightly-knit clusters. The clusters are capable of providing high levels of performance for file service, database management, or general purpose computing. Because Fibre Channel is able to span up to 10 kilometers between nodes, F/C allows very high-speed movement of data between systems that are greatly separated from one another.
Also, the F/C standard defines a layered protocol architecture consisting of five layers, the highest layer defining mappings from other communication protocols onto the F/C fabric.
The network behind the servers links one or more servers to one or more storage systems. Each storage system may be RAID (“Redundant Array of Inexpensive Disks”), tape backup, tape library, CD-ROM library, or JBOD (“Just a Bunch of Disks”).
Fibre Channel networks have proven robust and resilient, and include at least these features: shared storage among systems; scalable networking; high performance; fast data access and backup. In a Fibre Channel network, legacy storage systems are interfaced using a Fibre Channel to SCSI bridge. Fibre Channel standards include network features that provide required connectivity, distance, and protocol multiplexing. F/C also supports traditional channel features for simplicity, repeatable performance, and guaranteed delivery.
The Fibre Channel industry standards also provide for several different types, or classes, of data transfers. A class 1 transfer requires circuit switching, i.e., reserved data paths through the network switch, and generally involves the transfer of more than one frame, frequently numerous frames, between two identified network elements. In contrast, a class 2 transfer requires allocation of a path through the network switch for each transfer of a single frame from one network element to another. Frame switching for class 2 transfers is more difficult to implement that class 1 circuit switching because frame switching requires a memory mechanism for temporarily storing incoming frames in a source queue prior to their routing to a destination port, or a destination queue at a central destination port. A memory mechanism typically includes numerous input/output connections with associated support circuitry and queuing logic. Additional complexity and hardware is required when channels carrying data at different bit rates are to be interfaced.
At least one standard in connection with Fibre Channel technology imposes the requirement to maintain guaranteed in-order delivery of data frames across connecting links, regardless of cable distances (“Distance Standard”). As indicated, the Distance Standard cannot be satisfied using SCSI technology. Known striping methods for transmitting data frames across links include byte striping and word striping. Both have disadvantages in the Fibre Channel environment because of the high-speed requirements for data movement and transfer. Both byte striping and word striping require not only multiple links, but also that links remain open during transmission of data. As indicated, in an environment demanding significantly accelerated speeds of data movement, not all links will remain “open”; not all lanes consistently and continually will deliver frames at an appointed or expected point in proper sequence. The result has been described as a bottleneck, the inability of each successive frame to pass across each link in a prescribed or desired order or sequence.
To achieve the objective of sequential, in-order delivery of data frames across connecting links, existing methods and apparatus require that all cables and channels be similar in length. Otherwise, alignment problems attributable to delayed sequencing occur. Those skilled in the art sometimes refer to delayed sequencing of data in the form of frames as “jitter.” Existing technologies are unable to provide sufficient error management to overcome the problems of clogging, bottlenecks, and jitter.
The present invention eliminates the problems associated with byte and word striping; frame striping is employed. By directing successive data frames across links connecting entities in a F/C environment, load balancing is achieved across all links. As viewed by software associated with F/C technology, frame striping may be viewed or perceived as one vertical length or link; the links may be aggregated to simulate a unitary connection among the nodes. This eliminates the adverse consequences caused by variable link characteristics, including different cable lengths. Accordingly, problems associated at least with differences in length are avoided. Considering the pragmatic problems that impact operation of a F/C network, if one F/C link is cut or disable, the present invention will continue to stripe data frames across the remaining links. Thus, unlike the problems inherent in the conventional SCSI system, a disruption on one link will not affect operation of the system as a whole. The present invention quickly reallocates traffic across the links.
Inter-Element Links (“IEL's”); or Inter-Switch Links (“ISL's”) as they are sometimes referred to, between entities in a network system has, until now, proven to be a significant limiting factor to successful in-order data delivery in connection with the Delivery Standard. As the lengths change between points in the fabric, or between entities in the network, without the present invention the fabric must be reinitialized and new routing paths configured.
Therefore, a previously unaddressed need exists in the industry for a new, useful and reliable method and apparatus for aggregating links in networks, particularly in a Fibre Channel environment. It would be of considerable advantage to provide a method and apparatus that aggregates a plurality of links to simulate a unitary connection among one or more nodes in a fibre channel system, thus enabling in-order delivery of data frames across the plurality of links without reinitializing the fabric in a fibre channel system due to variations in link characteristics.